High-frequency inductor



Oct. 22, 1935. w. J. PQLYDVOROFF 2,018,626

HIGH FREQUENCY INDUCTOR Filed Kay 13, 1935 INVENTOR, MAD/MA? J $410020;

ATTORNEY.

Patented Oct. 22, 1935 UNITED STATES 2,018,628 HIGH-FREQUENCY INDUC'IOR Wladimir J. Poiydoroil, Chicago,

Johnson Laborattlisrieo, Inc., Chicago, Ill.

\ l oration of Illino Application May 13,

In Great Britain 13 Claims.

This invention relates to high-frequency inductors of the type which include comminuted magnetic cores for increasing the effective inductance of the windings at radio frequencies. Magnetic cores suitable for such frequencies consist of a compressed mass terial the particles of which are insulated from one another, as described for example in U. 8. Patent No. 1,982,689.

The object of the invention is to provide an improved construction for these ferro-magnetic cored inductors whereby the factor of merit (i. e., the ratio of inductance to effective highirequency resistance) be materially increased as compared with aircore coils, or the usual types of iron-core coils.

The invention consists essentially in the use in conjunction with a comminuted magnetic core of a plurality of windings of the flat-spiral or multi-layer type wound so that not more than a few turns lie adjacent the surface of the core,

the greater part of the winding being spaced from the surface of the core. The efiect of this arrangement is that losses due to the influence of adjacent turns of the winding on one another through the core material are greatly reduced,

since all but a few of the turns are well spaced from the surface of the core. It is found that the reduction of these losses is more than suflicient to compensate for the loss of inductance due to the relatively ineffective use of the core material as compared with the usual solenoidal coil wound close to the core.

A very desirable configuration of the magnetic fleld results when I employ a number of windings mounted coaxially upon a common core and spaced from one another along the magnetic axis. If these coils are wound with Litz wire, the copper losses can be reduced to an extremely low value, and I have found that it is possible to take full advantage of the efficiency of the Litz winding at frequencies of between 100 and 1500 kilocycles by the use of several coil sections spaced from one another in the direction of the magnetic axis and mounted coaxially with a magnetic core, provided the losses which occur in the core itself are made sufliciently low. In accordance with my invention, therefore, for the purpose of obtaining a high factor of merit for frequencies of from 100' to 1500 kilocycles per second, I construct an inductor in which the winding is composed of a number of multi-layer sections each wound with Litz wire and spaced from one another along the magnetic axis, the sections being mounted coaxially with a core of magnetic material, the degree of subdivision of which is so chosen in relation to the strand diameter of the Litz wire used that the core losses are approximately equal to the copper losses.

The invention will be more completely underof powdered magnetic mafor radio frequencies will IlL, assignor to 1935, Serial No. 21,166

February 2, 1934 stood from the following description taken in connection with the accompanying drawing, in which:

Figure l is a view, partly in section of an inductor embodying the invention, and

Figures 2 to 4 are similar views showing modifi cations.

In the construction illustrated in Figure 1 of the drawing, the winding l is divided into three bank-wound multi-Iayer sections 2, 3, and 4, which are supported and spaced from one another by means of ribs 5 formed integrally with a hollow cylindrical form 6 made of suitable insulating material.

. The magnetic core 1 is in the form of a cylindrical rod which is pushed into the form 6 so that it is linked with all the sections 2, 3, 4 of the winding I. To facilitate accurate adjustment of the inductance of the winding I, the core 1 is preferably arranged so that it can be adjusted axially relatively to the form 6, and for this purpose it is fixed to a screw-threaded rod 8 which engages in a suitableaxial tapped hole 8a formed in the material of the form 6 as shown, so that rotation of the core 1 relatively to the form 6 effects axial adjustment of the core I.

In the modified construction shown in Figure 2 of the drawing, the winding 9 has three sections III, II and If each of which consists of a self-supporting type of multi-layer winding, e. g. a universal winding mounted on a cupped cylindrical form l3, and which are spaced from one another in the direction of the magnetic axis. In this construction, the magnetic core I4 is a cylindrical rod which slides in the form I3. An additional yoke IS in the form of a U is employed and is adapted to engage the ends of the rod It so as to form a completely closed magnetic circuit linked with the winding. A screwthreaded and end-slotted rod 30 which engages in an axial hole 28 in the end of form l3 and is provided with lock nut 29, is fixedly attached to rod I I and provides for adjusting the rod it relatively to the form I! .and yoke l5, for the purpose of. adjusting the inductance of the inductor to the required value.

The construction shown in Figure 3 is similar to that illustrated in Figure 1 except that an additional outer core part it in the shape of a hollow cylinder flanged at both ends surrounds the form I! so as to produce a nearly completely closed magnetic circuit. The flanges it at the A suitable slot 21 may be formed in the end of the rod 2| to enable the rod to be adjusted by means of a screw-driver.

It will be apparent that in order to accomodate the spaced windings, the core will of necessity have considerable length. In general, its length should be not less than twice its diameter.

An essential feature of the construction of the inductor is the sub-division of the windings into a number of spaced sections in each of which not more than a'few turns lie adjacent the surface of the core.

In each of the constructions illustrated, the coil is divided into a number of multi-layer sections which are spaced from one another in the direction of the magnetic axis. These sections may be random wound in suitable slots in the iormer,or may be bank wound, or of the universal or other self. supporting type. The winding of the individual sections may also take various other forms, such as the fiat spiral or flat pancake type of 'winding. The greater the radial depth of the winding in comparison to its width the lower will be the losses due to the reaction of the turns of the through the material of the core. It is found however, that a flat spiral or very thin flat pancake type of winding is less eflicient than a shallower and wider winding, owing to the fact that the increase of inductance due to the iron core falls off as the radial depth of the winding is increased. The best results are obtained when the radial depth of each section is made not less than the width of the winding. Such windings may be described as having at least as many layers as turns. per layer.

In all cases the windings are preferably of Litz wire, and in order to obtain the benefit of the extremely low copper losses at high frequencies due to the use of Litz wire, the degree of sub-division of the magnetic material of the core must bear a definite relation to the diameter of the strands of Litz wire used. If this relation is observed the core losses will be approximately equal to the copper and dielectric losses.

The actual sizes of the core particles and thicknesses of the strands of the Litz wire may vary within certain limits, according to the frequencies for which the coil is intended. The following table indicates suitable core particle sizes for three ranges of frequencies which, taken together, comprise the whole of the normal broadcast frequency band.

Frequency band ggg Kilocuclea per second Micrzms 500 5 to 30 5001,000 2 to 10 l,000-1,500 0. 5 to 3 strand diameter for a winding on one another grain size and strand diameter results in core losses which are approximately equal to the copper and dielectric losses. Obviously, a smaller given core particle size would not result in a reduced factor of merit. but if the strand diameter and core particle size are ill matched, either the copper losses or core losses will preponderate unduly, and the greater efilciency which might have been obtained with the wire and core material properly chosen will be lost.

Having thus described my invention, what I claim is:

l. A high-frequency inductor comprising a compressed comminuted term-magnetic core having a length at least twice its diameter, and a plurality of serially connected windings of stranded conductor, each of said windings having at least as many layers as turns per layer and being mutually spaced lengthwise of said core the size of the particles in said core and of the strands crons in size, and a plurality of serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said core.

3. An inductor for use in the frequency range between 500 and 1000 kilocycles per second comprising a compressed comminuted ferro-magnetic core having a length at least twice its diameter and having particles varying from 2 to 10 microns in size, and a plurality of serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said core.

4. An inductor for use in the frequency range between 1000 and 1500 kilocycles per second comhaving a length at least twice its diameter, and a plurality of serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said core,'said core and said windings being so proportioned that the losses in said core are substantially equa to the total losses in said windmgs.

6. A high-frequency inductor comprising a compressed comminuted ferro-magnetic core having a length at least twice its diameter, a screw-threaded member in said core, an insulating form having a threaded hole to receive said screw-threaded member, and a plurality of serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said form, said core being positioned within said form, and being adjustable lengthwise of said form to establish the inductance of said inductor at a desired value.

7. A high-frequency inductor comprising a compressed comminuted term-magnetic core having a length at least twice its diameter, a plurality oi serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said core, and a term-magnetic yoke magnetically joining the ends 01' said core.

8. A high-frequency inductor comprising a compressed comminuted term-magnetic core having a length at least twice its diameter, a plurality of serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said core, a term-magnetic yoke magnetically joining the ends of said core, and means for adjusting said core lengthwise to establish the inductance of said inductor at a desired value.

9. A high-frequency inductor comprising a compressed comminuted term-magnetic core having a length at least twice its diameter, a plurality o1 serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said core, and plural compressed comminuted ferro-magnetic yoke members which magnetically Join the ends of said core.

10. A high-frequency inductor comprising a compressed comminuted term-magnetic core having a length at least twice its diameter and provided with a threaded portion, an insulating iorm threaded internally to receive said threaded portion of the core, and a plurality oi serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said form.

11. A high-frequency inductor comprising a compressed comminuted term-magnetic core having a length at least twice its diameter and provided with a threaded portion, an insulating form threaded internally to receive said threaded portion of the core, a plurality of serially connected windings each having at least as many layers as turns per layer and being mutually spaced lengthwise of said form, and plural compressed comminuted term-magnetic yoke members which magnetically join the ends of said core.

12. A high-frequency inductor for use in the frequency range between 100 and 1500 kilocycles per second comprising a core of compressed ferromagnetic particles and having a length at least twice its diameter, and a plurality of serially connected windings each having at least as many layers as turns per layer wound with a conductor having plural insulated strands andbeing mutually spaced lengthwise of said core, the diameter of said strands being approximately 10 times the average size of said particles.

13. A high-frequency inductor comprising a core of compressed individually insulated ferromagnetic particles, and a plurality of serially connected windings wound with a conductor having plural insulated strands, the diameter of said strands being approximately 10 times the average size 'otsaid particles.

' WLADIMIR J. POLYDOROFF. 

